Despite advances in science, tornadoes take deadly toll

Members of the St. Louis Metro Urban Search & Rescue Strike Team 3 conduct a secondary search for victims of a tornado after it struck Joplin, Missouri, May 24, 2011.

CHICAGO (Reuters) - It is one of the terrible paradoxes of this spring's deadly spate of U.S. tornadoes.

Engineers know how to build shelters that provide extensive protection from tornadoes, and weather forecasting advances make it easier than ever for experts to predict, spot and track twisters.

Yet 2011 is on pace to be one of the deadliest tornado seasons in history. Why?

In the average year, 62 Americans are killed by twisters, according to the Federal Emergency Management Agency. So far this year, more than 480 have died -- and the tornado season, which runs from April through July, is only half over.

Experts say a number of factors are contributing to the extraordinary death toll, including that some people are simply in the wrong place at the wrong time.

"When a killer wind directly hits a population, people are likely going to die," said Brian Ancell, a researcher with the atmospheric science group at Texas Tech University.

Nineteen states are in what officials term "Wind Zone IV," an area that has experienced the most consistent and strongest tornado activity. Among the 19 are several with large populations including Texas, Illinois, Ohio and Michigan.

People who live in these states have put themselves in harm's way because there is a rare but real possibility of wind storms of incredible destructive power, so-called EF4 and EF5 tornadoes on the Enhanced Fujita Scale.

AIRBORNE MISSILES

Tornadoes in Tuscaloosa, Alabama and Joplin, Missouri were both rated at EF4, according to the National Weather Service.

Larry Tanner, a tornado damage expert at the Wind Engineering Research Center at Texas Tech, said a powerful tornado can turn strong frame houses, reinforced concrete structures, automobiles and trees into airborne missiles.

"The wind pressure from the tornado starts a chain reaction of structural failure," Tanner said, "and as that material becomes part of the funnel cloud it becomes a grinder on other buildings downwind."

In the case of Joplin, deadly winds of nearly 200 miles per hour roared through the city of about 50,000 just on Sunday evening, killing at least 118 people.

Building codes in most parts of the United States -- even in those areas prone to the deadliest tornadoes -- only require homes to withstand winds up to 90 miles an hour, about an EF1 tornado, according to Tanner.

As a result, walls, ceilings, doors and other parts of the home often cannot endure the most extreme windstorms.

"When you have a tornado that hits the heart of a city … it's almost next to impossible to not have as many fatalities as we had," said Yasamie August, spokeswoman for the Alabama Emergency Management Agency.

BUILD A SAFE ROOM

But officials insist that with proper planning, residents of areas that take a direct hit from the most destructive tornadoes on record can have "a high probability of being protected from injury or death."

FEMA has a 64-page pamphlet titled "Taking Shelter From the Storm" with instructions on how to build a safe room within an existing structure that can endure winds and windborne debris of up to 250 miles an hour. (here).

At about $5,000, the rooms are not cheap. But several states offer rebates to home and business owners who build safe rooms that meet the FEMA standards -- and Tommy Jackson, a spokesman for the Arkansas Department of Emergency Management, said the rooms were "getting very popular" as a result of this season's deadly string of storms.

Jackson and others say one issue they continue to deal with this year, and which helps account for some of the avoidable deaths the twisters cause, is tornado-warning fatigue.

Forecasters at places like the National Storm Center have gotten very good at predicting tornadoes and issue hundreds of watches and warnings each season.

Few of them ever turn into the kinds of violent monster tornadoes that devastated Joplin this week and tore through Tuscaloosa last month.

As a result, some people -- even in tornado-prone areas -- have stopped taking the warnings seriously.

Jackson acknowledges the problem of false predictions but warns that it is always better to err on the side of caution.

"The stakes are too high," he said. "People need to treat any tornado warning like it's the real deal."

(Additional reporting by Colleen Jenkins; Editing by Greg McCune)